INDUCTION HEATING DEVICE AND METHOD OF CONTROLLING THE SAME

Abstract

The disclosure relates to an induction heating device and a method of controlling the induction heating device. The induction heating device includes a first working coil and a second working coil. According to an embodiment of the disclosure, a driving start time of the first working coil and a driving start time of the second working coil are determined based on a driving scheme of the first working coil, a driving scheme of the second working coil, and a predetermined driving period. According to an embodiment of the disclosure, an eccentricity determination period of the first working coil and an eccentricity determination period of the second working coil are determined based on the driving scheme of the first working coil, the driving scheme of the second working coil, the driving period, a duty cycle of the first working coil, and a duty cycle of the second working coil.

Claims

1. A method of controlling an induction heating device, the method comprising: determining a driving scheme and duty cycle of a first working coil according to a required power value for the first working coil; determining a driving scheme and duty cycle of a second working coil according to a required power value for the second working coil; determining a driving start time of the first working coil and a driving start time of the second working coil based on the driving scheme of the first working coil, the driving scheme of the second working coil, and a predetermined driving period; determining an eccentricity determination period of the first working coil and an eccentricity determination period of the second working coil based on the driving scheme of the first working coil, the driving scheme of the second working coil, the driving period, the duty cycle of the first working coil, and the duty cycle of the second working coil; driving each of the first working coil and the second working coil according to the driving scheme and the driving start times; determining eccentricity of a vessel placed on the first working coil according to the eccentricity determination period of the first working coil; and determining eccentricity of a vessel placed on the second working coil according to the eccentricity determination period of the second working coil.

2. The method of claim 1, wherein if the required power values are a predetermined reference power value, the driving scheme is determined to be a linear driving scheme and, if the required power values are less than the predetermined reference power value, the driving scheme is determined to be a duty driving scheme.

3. The method of claim 1, wherein if a driving scheme of the first working coil is a linear driving scheme, and a driving scheme of the second working coil is a linear driving scheme, the driving start time of the first working coil is set to be identical to the driving period, and the driving start time of the second working coil is set to be identical to ½ of the driving period.

4. The method of claim 1, wherein if a driving scheme of the first working coil is a linear driving scheme, and a driving scheme of the second working coil is a linear driving scheme, the eccentricity determination period of the first working coil is set to be identical to ½ of the driving period, and the eccentricity determination period of the second working coil is set to identical to the driving period.

5. The method of claim 1, wherein if a driving scheme of the first working coil is a linear driving scheme, and a driving scheme of the second working coil is a duty driving scheme, the driving start time of the first working coil is set to be identical to the driving period, and the driving start time of the second working coil is set to be identical to the driving period less an on-time of the second working coil.

6. The method of claim 1, wherein if a driving scheme of the first working coil is a linear driving scheme, and a driving scheme of the second working coil is a duty driving scheme, the eccentricity determination period of the first working coil is set to be identical to ½ of an off-time of the second working coil, and the eccentricity determination period of the second working coil is set to identical to ½ of an on-time of the second working coil.

7. The method of claim 1, wherein if a driving scheme of the first working coil is a duty driving scheme, and a driving scheme of the second working coil is a duty driving scheme, the driving start time of the first working coil is set to be identical to the driving period, and the driving start time of the second working coil is set to be identical to the driving period less an on-time of the second working coil.

8. The method of claim 1, wherein if a driving scheme of the first working coil is a duty driving scheme, and a driving scheme of the second working coil is a duty driving scheme, the eccentricity determination period of the first working coil and the eccentricity determination period of the second working coil are set to differ depending on an on-time of the first working coil and an on-time of the second working coil.

9. The method of claim 8, wherein if the on-time of the first working coil is larger than ½ of the driving period, and the on-time of the second working coil is equal or larger than ½ of the driving period, the eccentricity determination period of the first working coil is set to be identical to ½ of an off-time of the second working coil, and the eccentricity determination period of the second working coil is set to be identical to an off-time of the first working coil.

10. The method of claim 8, wherein if the on-time of the first working coil is larger than ½ of the driving period, and the on-time of the second working coil is smaller than ½ of the driving period, the eccentricity determination period of the first working coil is set to be identical to ½ of the on-time of the first working coil, and the eccentricity determination period of the second working coil is set to be identical to ½ of the on-time of the second working coil.

11. The method of claim 8, wherein if the on-time of the first working coil is smaller than ½ of the driving period, the eccentricity determination period of the first working coil is set to be identical to ½ of the on-time of the first working coil, and the eccentricity determination period of the second working coil is set to be identical to ½ of the on-time of the second working coil.

12. The method of claim 8, wherein if the on-time of the first working coil is equal to ½ of the driving period, and the on-time of the second working coil is equal or smaller than ½ of the driving period, the eccentricity determination period of the first working coil is set to be identical to ½ of the on-time of the first working coil, and the eccentricity determination period of the second working coil is set to be identical to ½ of the on-time of the second working coil.

13. The method of claim 8, wherein if the on-time of the first working coil is equal to ½ of the driving period, and the on-time of the second working coil is larger than ½ of the driving period, the eccentricity determination period of the first working coil is set to be identical to ½ of an off-time of the second working coil, and the eccentricity determination period of the second working coil is set to be identical to ½ of an off-time of the first working coil.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0041] A more complete appreciation of the present disclosure and many of the attendant aspects thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

[0042] FIG. 1 illustrates an example in which a vessel is placed on a heating area of an induction heating device according to the prior art;

[0043] FIGS. 2, 3, 4, 5, and 6 illustrate variations in the eccentricity determination period of a vessel placed on each working coil and the output power of each working coil when a first working coil and a second working coil of an induction heating device are driven according to the prior art;

[0044] FIG. 7 illustrates a configuration of an induction heating device according to an embodiment of the disclosure;

[0045] FIG. 8 illustrates variations in the eccentricity determination period of a vessel placed on each working coil and the output power of each working coil when a first working coil of an induction heating device is linearly driven, and a second working coil of the induction heating device is linearly driven, according to an embodiment of the disclosure;

[0046] FIGS. 9, 10, and 11 illustrate variations in the eccentricity determination period of a vessel placed on each working coil and the output power of each working coil when a first working coil of an induction heating device is linearly driven, and a second working coil of the induction heating device is duty-driven, according to an embodiment of the disclosure;

[0047] FIGS. 12, 13, and 14 illustrate variations in the eccentricity determination period of a vessel placed on each working coil and the output power of each working coil when a first working coil of an induction heating device is duty-driven, an on-time of the first working coil is larger than ½ of a driving period, and a second working coil of the induction heating device is duty-driven, according to an embodiment of the disclosure;

[0048] FIGS. 15, 16, and 17 illustrate variations in the eccentricity determination period of a vessel placed on each working coil and the output power of each working coil when a first working coil of an induction heating device is duty-driven, an on-time of the first working coil is smaller than ½ of a driving period, and a second working coil of the induction heating device is duty-driven, according to an embodiment of the disclosure;

[0049] FIGS. 18, 19, and 20 illustrate variations in the eccentricity determination period of a vessel placed on each working coil and the output power of each working coil when a first working coil of an induction heating device is duty-driven, an on-time of the first working coil is equal to ½ of a driving period, and a second working coil of the induction heating device is duty-driven, according to an embodiment of the disclosure; and

[0050] FIG. 21 is a flowchart illustrating a method of controlling an induction heating device according to an embodiment of the disclosure.

MODE FOR THE INVENTION

[0051] The foregoing objectives, features, and advantages are described below in detail with reference to the accompanying drawings so that the technical spirit of the disclosure may easily be achieved by one of ordinary skill in the art to which the invention pertains. When determined to make the subject matter of the disclosure unclear, the detailed description of the known art or functions may be skipped. Hereinafter, preferred embodiments of the disclosure are described in detail with reference to the accompanying drawings. The same reference denotations are used to refer to the same or similar elements throughout the drawings.

[0052] FIG. 7 illustrates a configuration of an induction heating device according to an embodiment of the disclosure.

[0053] Referring to FIG. 7, according to an embodiment of the disclosure, an induction heating device 2 includes a rectifying circuit 204, a smoothing circuit L, C1, a first working coil WC1, a second working coil WC2, inverter circuits, a control circuit 20, and a driving circuit 21.

[0054] The induction heating device 2 is driven by power supplied from an input power source 202. The rectifying circuit 204 rectifies an alternating current (AC) input voltage supplied from the input power source 202 and outputs a pulse waveform of voltage.

[0055] The smoothing circuit L, C1 smooths the voltage rectified by the rectifying circuit 204 and outputs a direct current (DC) link voltage. The smoothing circuit L, C1 includes an inductor L and a DC link capacitor C1.

[0056] The inverter circuits converts the DC link voltage output from the smoothing circuit L, C1 into an AC voltage for driving each working coil WC1 and WC2. A first inverter circuit includes a first capacitor C2, a second capacitor C3, a first switching element SW1, and a second switching element SW2. A second inverter circuit includes a third capacitor C4, a fourth capacitor C5, a third switching element SW3, and a fourth switching element SW4.

[0057] The first switching element SW1 and the second switching element SW2 are alternately turned on/off by a first inverter driving signal S1 and a second inverter driving signal S2 output from the driving circuit 21. The third switching element SW3 and the fourth switching element SW4 are alternately turned on/off by a third inverter driving signal S3 and a fourth inverter driving signal S4 output from the driving circuit 21.

[0058] The first inverter driving signal S1, the second inverter driving signal S2, the third inverter driving signal S3, and the fourth inverter driving signal S4 each are a pulse width modulation (PWM) signal with a predetermined duty cycle. If the first inverter driving signal S1 and the second inverter driving signal S2 are applied to the first switching element SW1 and the second switching element SW2, respectively, the first switching element SW1 and the second switching element SW2 are alternately turned on/off so that the DC link voltage is converted into an AC voltage. If the third inverter driving signal S3 and the fourth inverter driving signal S4 are applied to the third switching element SW3 and the fourth switching element SW4, respectively, the third switching element SW3 and the fourth switching element SW4 are alternately turned on/off so that the DC link voltage is converted into an AC voltage.

[0059] The AC voltages output from the inverter circuits are applied to the working cols WC1 and WC2. If the AC voltages are applied, the working coils WC1 and WC2 are driven. If the working coils WC1 and WC2 are driven, eddy currents flow through the vessels placed on the working coils WC1 and WC2, thereby heating the vessels. When the working coils WC1 and WC2 are driven, the magnitude of thermal energy supplied to the vessels is varied depending on the magnitude of power produced by the working coils WC1 and WC2, i.e., the output power values of the working coils.

[0060] The control circuit 20 determines the respective driving frequencies of the inverter circuits and supplies control signals corresponding to the determined driving frequencies to the driving circuit 21. The driving circuit 21 outputs inverter driving signals S1 to S4 with duty cycles corresponding to the driving frequencies determined by the control circuit 20.

[0061] The user places vessels on the working coils WC1 and WC2 of the induction heating device and sets heating levels for the vessels, thereby issuing heating start commands to the working coils WC1 and WC2. If the user issues the heating start commands, output power values required for the working coils WC1 and WC2, i.e., required power values, are determined depending on the heating levels set by the user.

[0062] Receiving the user's heating start commands, the control circuit 20 sets driving frequencies corresponding to the required power values and supplies control signals corresponding to the set driving frequencies to the driving circuit 21. Thus, the inverter driving signals S1 to S4 are output from the driving circuit 21 so that the working coils WC1 and WC2 are driven. As the working coils WC1 and WC2 are driven, the vessels placed by the user are heated.

[0063] If the user's heating commands are input, the control circuit 20 drives each working coil WC1 and WC2 based on a predetermined driving period T.

[0064] The control circuit 20 determines a driving scheme (e.g., linear driving or duty driving) and duty cycle for each working coil WC1 and WC2 based on the required power value for each working coil WC1 and WC2 set by the user's heating commands. For example, if the required power value for each working coil WC1 and WC2 is a predetermined reference power value (e.g., 500 W) or more, the working coil is linearly driven. For example, if the required power value for the first working coil is determined to be 1,000 W, the first working coil is linearly driven to continuously deliver a power of 1,000 W as shown in FIG. 2.

[0065] In contrast, if the required power value for the working coil is less than the reference power value, the working coil is duty-driven. For example, if the required power value for the first working coil is determined to be 400 W, the first working coil is driven while repeating its on and off states based on the duty cycle corresponding to the required power value as shown in FIG. 3.

[0066] If the driving scheme of each working coil WC1 and WC2 is determined to be a duty driving scheme, the duty cycle of each working coil WC1 and WC2 may be set to differ depending on the required power value. As the required power value increases, a larger duty cycle is set, and a longer on-time is set for the working coil.

[0067] When the working coils WC1 and WC2 are driven, the control circuit 20 obtains an input voltage measured by a voltage sensor 22 and an input current measured by a current sensor 23. The control circuit 20 may calculate the magnitude of power supplied to the working coils WC1 and WC2, i.e., input power values of the working coils WC1 and WC2, based on the obtained input voltage and input current.

[0068] The control circuit 20 may compare the calculated input power value of each working coil WC1 and WC2 with a predetermined reference value, thereby determining the eccentricity of the vessel placed on each working coil WC1 and WC2. For example, if the input power value measured while the first working coil WC1 is driven is larger than the reference value, the control circuit 20 may determine that the vessel placed on the first working coil WC1 is in eccentricity.

[0069] According to an embodiment, the control circuit 20 may compare the input current measured by the current sensor 23 with a predetermined reference value, thereby determining the eccentricity of the vessel placed on each working coil WC1 and WC2. For example, if the input current value measured while the first working coil WC1 is driven is larger than the reference value, the control circuit 20 may determine that the vessel placed on the first working coil WC1 is in eccentricity.

[0070] The control circuit 20 temporarily stops driving the other working coil than the working coil which is the target for determining the eccentricity of the vessel. For example, the control circuit 20 temporarily stops driving the second working coil WC2 at the time of determining the eccentricity of the vessel placed on the first working coil WC1.

[0071] Described below is an example driving process of an induction heating device according to the user's input of heating commands. Although an embodiment is described below in which a vessel is placed on each of the first working coil WC1 and the second working coil WC2 of the induction heating device, and heating commands are then input, the method of controlling an induction heating device may also apply to induction heating devices with three or more working coils according to an embodiment of the disclosure.

[0072] If the user sets a heating level for the vessel placed on each of the first working coil WC1 and the second working coil WC2 through a control panel of the induction heating device, a heating command for each of the first working coil WC1 and the second working coil WC2 is input.

[0073] The control circuit 20 determines a required power value corresponding to the heating level which the user has set for each working coil. The control circuit 20 determines that the driving scheme of each working coil is a linear driving scheme or duty driving scheme according to the required power value of each working coil. If the required power value is a reference power value or more, the driving scheme of the working coil is determined to be a linear driving scheme and, if the required power value is smaller than the reference power value, the driving scheme of the working coil is determined to be a duty driving scheme.

[0074] If the driving scheme of the working coil is determined to be a duty driving scheme, the control circuit 20 determines the duty cycle of the working coil, i.e., the on-time and off-time of the working coil during a predetermined driving period T, according to the required power value of the working coil. As the required power value increases, a larger duty cycle is set, and a longer on-time is set for the working coil.

[0075] The control circuit 20 starts a driving start time of each working coil based on the determined driving scheme of each working coil and the predetermined driving period T. The control circuit 20 determines the eccentricity determination period of each working coil based on the driving scheme of each working coil, driving period T, and the duty cycle of each working coil.

[0076] Now described with reference to FIGS. 8 to 20 are embodiments in which the control circuit 20 sets the driving start time and eccentricity determination period of each working coil according to the driving scheme and duty cycle of each working coil.

[0077] FIG. 8 illustrates variations in the eccentricity determination period of a vessel placed on each working coil and the output power of each working coil when a first working coil of an induction heating device is linearly driven, and a second working coil of the induction heating device is linearly driven, according to an embodiment of the disclosure.

[0078] According to an embodiment of the disclosure, if the driving schemes of the first working coil WC1 and the second working coil WC2 are both determined to be a linear driving scheme, the driving start time of the first working coil WC1 is set to be identical to a predetermined driving period T, and the driving start time of the second working coil WC2 is set to be identical to ½ of the driving period T.

[0079] If the driving schemes of the first working coil WC1 and the second working coil WC2 are both determined to be a linear driving scheme as shown in FIG. 8, the eccentricity determination period DA of the first working coil WC1 is set to be identical to ½ of the driving period T, and the eccentricity determination period DB of the second working coil WC2 is set to be identical to the driving period T.

[0080] The control circuit 20 drives the first working coil WC1 and the second working coil WC2 based on the determined driving start times and eccentricity determination periods. As shown in FIG. 8, the second working coil WC2 temporarily stops running at the eccentricity determination times DA and 2DA of the vessel placed on the first working coil WC1 (812 and 814), and the first working coil WC1 temporarily stops running at the eccentricity determination times DB and 2DB of the vessel placed on the second working coil WC2 (802 and 804).

[0081] FIGS. 9, 10, and 11 illustrates variations in the eccentricity determination period of a vessel placed on each working coil and the output power of each working coil when a first working coil of an induction heating device is linearly driven, and a second working coil of the induction heating device is duty-driven, according to an embodiment of the disclosure.

[0082] In the embodiments of FIGS. 9, 10, and 11, the first working coil WC1 is linearly driven. In the embodiments of FIGS. 9, 10, and 11, the second working coil WC2 is duty-driven based on different duty cycles. In the embodiment of FIG. 9, the on-time of the second working coil WC2 is set to be smaller than ½ of the driving period T. In the embodiment of FIG. 10, the on-time of the second working coil WC2 is set to be identical to ½ of the driving period T. In the embodiment of FIG. 11, the on-time of the second working coil WC2 is set to be larger than ½ of the driving period T.

[0083] According to an embodiment of the disclosure, if the first working coil WC1 is linearly driven, and the second working coil WC2 is duty-driven, the driving start time of the first working coil WC1 is set to be identical to the driving period P, and the driving start time of the second working coil WC2 is set to be identical to the driving period T less the on-time of the second working coil.

[0084] If the first working coil WC1 is linearly driven, and the second working coil WC2 is duty-driven as shown in FIGS. 9 to 11, the eccentricity determination period DA of the first working coil WC1 is set to be identical to ½ of the off-time of the second working coil, and the eccentricity determination period DB of the second working coil WC2 is set to be identical to ½ of the on-time of the second working coil WC2.

[0085] The control circuit 20 drives the first working coil WC1 and the second working coil WC2 based on the determined driving start times and eccentricity determination periods. As shown in FIGS. 9 to 11, the first working coil WC1 temporarily stops running at the eccentricity determination times DB and 2DB of the vessel placed on the second working coil WC2 (902, 904, 1002, 1004, 1102, and 1104).

[0086] Since the eccentricity determination times DA and 2DA of the first working coil WC1 both are set to fall within the off-time of the second working coil WC2 as shown in FIGS. 9, 10, and 11, the second working coil WC2 is prevented from forced stop when the eccentricity of the vessel placed on the first working coil WC1 is determined. Thus, power supply by the second working coil WC2 may be performed stably.

[0087] FIGS. 12, 13, and 14 illustrate variations in the eccentricity determination period of a vessel placed on each working coil and the output power of each working coil when a first working coil of an induction heating device is duty-driven, an on-time of the first working coil is larger than ½ of a driving period, and a second working coil of the induction heating device is duty-driven, according to an embodiment of the disclosure.

[0088] In the embodiments of FIGS. 12, 13, and 14, the first working coil WC1 and the second working coil WC2 both are duty-driven.

[0089] In the embodiments of FIGS. 12, 13, and 14, the on-time of the first working coil WC1 is set to be larger than ½ of the driving period T.

[0090] In the embodiment of FIG. 12, the on-time of the second working coil WC2 is set to be smaller than ½ of the driving period T. In the embodiment of FIG. 13, the on-time of the second working coil WC2 is set to be identical to ½ of the driving period T. In the embodiment of FIG. 14, the on-time of the second working coil WC2 is set to be larger than ½ of the driving period T.

[0091] According to an embodiment of the disclosure, if the driving schemes of the first working coil WC1 and the second working coil WC2 are both determined to be a duty driving scheme, the driving start time of the first working coil WC1 is set to be identical to the driving period P, and the driving start time of the second working coil WC2 is set to be identical to the driving period T less the on-time of the second working coil WC2.

[0092] If the on-time of the first working coil WC1 is larger than ½ of the driving period T, and the on-time of the second working coil WC2 is smaller than ½ of the driving period T as shown in FIG. 12, the eccentricity determination period DA of the first working coil WC1 is set to be identical to ½ of the on-time of the first working coil WC1, and the eccentricity determination period DB of the second working coil WC2 is set to be identical to ½ of the on-time of the second working coil WC2.

[0093] If the on-time of the first working coil WC1 is larger than ½ of the driving period T, and the on-time of the second working coil WC2 is equal or larger than ½ of the driving period T as shown in FIGS. 13 and 14, the eccentricity determination period DA of the first working coil WC1 is set to be identical to ½ of the off-time of the second working coil WC2, and the eccentricity determination period DB of the second working coil WC2 is set to be identical to ½ of the off-time of the first working coil WC1.

[0094] The control circuit 20 drives the first working coil WC1 and the second working coil WC2 based on the determined driving start times and eccentricity determination periods. Since the eccentricity determination times DA and 2DA of the first working coil WC1 both are set to fall within the off-time of the second working coil WC2 as shown in FIGS. 12, 13, and 14, the second working coil WC2 is prevented from forced stop when the eccentricity of the vessel placed on the first working coil WC1 is determined. Since the eccentricity determination times DB and 2DB of the second working coil WC2 both are set to fall within the off-time of the first working coil WC1, the first working coil WC1 is prevented from forced stop when the eccentricity of the vessel placed on the second working coil WC2 is determined.

[0095] Thus, power supply by the first working coil WC1 and the second working coil WC2 may be performed stably.

[0096] FIGS. 15, 16, and 17 illustrate variations in the eccentricity determination period of a vessel placed on each working coil and the output power of each working coil when a first working coil of an induction heating device is duty-driven, an on-time of the first working coil is smaller than ½ of a driving period, and a second working coil of the induction heating device is duty-driven, according to an embodiment of the disclosure.

[0097] In the embodiments of FIGS. 15, 16, and 17, the on-time of the first working coil WC1 is set to be smaller than ½ of the driving period T.

[0098] In the embodiment of FIG. 15, the on-time of the second working coil WC2 is set to be smaller than ½ of the driving period T. In the embodiment of FIG. 16, the on-time of the second working coil WC2 is set to be identical to ½ of the driving period T. In the embodiment of FIG. 17, the on-time of the second working coil WC2 is set to be larger than ½ of the driving period T.

[0099] According to an embodiment of the disclosure, if the driving schemes of the first working coil WC1 and the second working coil WC2 are both determined to be a duty driving scheme, the driving start time of the first working coil WC1 is set to be identical to the driving period P, and the driving start time of the second working coil WC2 is set to be identical to the driving period T less the on-time of the second working coil WC2.

[0100] If the on-time of the first working coil WC1 is smaller than ½ of the driving period T as shown in FIGS. 15, 16, and 17, the eccentricity determination period DA of the first working coil WC1 is set to be identical to ½ of the on-time of the first working coil WC1, and the eccentricity determination period DB of the second working coil WC2 is set to be identical to ½ of the on-time of the second working coil WC2 regardless of the on-time of the second working coil WC2.

[0101] The control circuit 20 drives the first working coil WC1 and the second working coil WC2 based on the determined driving start times and eccentricity determination periods. Since the eccentricity determination times DA and 2DA of the first working coil WC1 both are set to fall within the off-time of the second working coil WC2 as shown in FIGS. 15, 16, and 17, the second working coil WC2 is prevented from forced stop when the eccentricity of the vessel placed on the first working coil WC1 is determined. Since the eccentricity determination times DB and 2DB of the second working coil WC2 both are set to fall within the off-time of the first working coil WC1, the first working coil WC1 is prevented from forced stop when the eccentricity of the vessel placed on the second working coil WC2 is determined.

[0102] Thus, power supply by the first working coil WC1 and the second working coil WC2 may be performed stably.

[0103] FIGS. 18, 19, and 20 illustrate variations in the eccentricity determination period of a vessel placed on each working coil and the output power of each working coil when a first working coil of an induction heating device is duty-driven, an on-time of the first working coil is equal to ½ of a driving period, and a second working coil of the induction heating device is duty-driven, according to an embodiment of the disclosure.

[0104] In the embodiments of FIGS. 18, 19, and 20, the first working coil WC1 and the second working coil WC2 both are duty-driven.

[0105] In the embodiments of FIGS. 18, 19, and 20, the on-time of the first working coil WC1 is set to be identical to ½ of the driving period T.

[0106] In the embodiment of FIG. 18, the on-time of the second working coil WC2 is set to be smaller than ½ of the driving period T. In the embodiment of FIG. 19, the on-time of the second working coil WC2 is set to be identical to ½ of the driving period T. In the embodiment of FIG. 20, the on-time of the second working coil WC2 is set to be larger than ½ of the driving period T.

[0107] According to an embodiment of the disclosure, if the driving schemes of the first working coil WC1 and the second working coil WC2 are both determined to be a duty driving scheme, the driving start time of the first working coil WC1 is set to be identical to the driving period P, and the driving start time of the second working coil WC2 is set to be identical to the driving period T less the on-time of the second working coil WC2.

[0108] If the on-time of the first working coil WC1 is equal to ½ of the driving period T, and the on-time of the second working coil WC2 is equal or smaller than ½ of the driving period T as shown in FIGS. 18 and 19, the eccentricity determination period DA of the first working coil WC1 is set to be identical to ½ of the on-time of the first working coil WC1, and the eccentricity determination period DB of the second working coil WC2 is set to be identical to ½ of the on-time of the second working coil WC2.

[0109] If the on-time of the first working coil WC1 is equal to ½ of the driving period T, and the on-time of the second working coil WC2 is larger than ½ of the driving period T as shown in FIG. 20, the eccentricity determination period DA of the first working coil WC1 is set to be identical to ½ of the off-time of the second working coil WC2, and the eccentricity determination period DB of the second working coil WC2 is set to be identical to ½ of the off-time of the first working coil WC1.

[0110] The control circuit 20 drives the first working coil WC1 and the second working coil WC2 based on the determined driving start times and eccentricity determination periods. Since the eccentricity determination times DA and 2DA of the first working coil WC1 both are set to fall within the off-time of the second working coil WC2 as shown in FIGS. 18, 19, and 20, the second working coil WC2 is prevented from forced stop when the eccentricity of the vessel placed on the first working coil WC1 is determined. Since the eccentricity determination times DB and 2DB of the second working coil WC2 both are set to fall within the off-time of the first working coil WC1, the first working coil WC1 is prevented from forced stop when the eccentricity of the vessel placed on the second working coil WC2 is determined.

[0111] Thus, power supply by the first working coil WC1 and the second working coil WC2 may be performed stably.

[0112] As described above in connection with the embodiments of FIGS. 8 to 20, if the driving start time and eccentricity determination time of each of the first working coil WC1 and the second working coil WC2 are determined, the control circuit 20 drives each of the first working coil WC1 and the second working coil WC2 according to the determined driving scheme and driving start time of each working coil.

[0113] Thereafter, the control circuit 20 determines the eccentricity of the vessel placed on each working coil according to the prior-determined eccentricity determination time of each working coil. In other words, the control circuit 20 determines the eccentricity of the vessel placed on the first working coil WC1 at each eccentricity determination time DA and 2DA of the first working coil WC1 and determines the eccentricity of the vessel placed on the second working coil WC2 at each eccentricity determination time DB and 2DB of the second working coil WC2.

[0114] If the respective driving start times and eccentricity determination times of the first working coil WC1 and the second working coil WC2 are determined as set forth above in connection with the embodiments of FIGS. 8 to 20, the eccentricity determination time of the first working coil WC1 and the eccentricity determination time of the second working coil WC2 do not overlap each other and, thus, such an occasion may be avoided where determination of eccentricity is rendered impossible due to an overlap between eccentricity determination times. Further, upon determining the eccentricity of the vessel placed on each working coil, the other working coil is prevented from forced stop, and this ensures stable supply of power to each working coil.

[0115] FIG. 21 is a flowchart illustrating a method of controlling an induction heating device according to an embodiment of the disclosure.

[0116] Referring to FIG. 21, according to an embodiment of the disclosure, a control circuit 20 of an induction heating device 2 determines a driving scheme and duty cycle of a first working coil WC1 according to a required power value for the first working coil WC1 (2102). The control circuit 20 determines a driving scheme and duty cycle of a second working coil WC2 according to a required power value for the second working coil WC2 (2104).

[0117] According to an embodiment of the disclosure, if the required power value for the working coil is a predetermined reference power value, the driving scheme of the working coil is determined to be a linear driving scheme and, if the required power value for the working coil is less than the predetermined reference power value, the driving scheme of the working coil is determined to be a duty driving scheme.

[0118] According to an embodiment of the disclosure, if the driving scheme of the working coil is a linear driving scheme, the duty cycle of the working coil is determined to be 100%. If the driving scheme of the working coil is a duty driving scheme, the duty cycle of the working coil is determined to differ depending on the required power value for the working coil.

[0119] The control circuit 20 determines the driving start time of the first working coil WC1 and the driving start time of the second working coil WC2 based on the driving scheme of the first working coil WC1, the driving scheme of the second working coil WC2, and a predetermined driving period T.

[0120] Then, the control circuit 20 determines the eccentricity determination period of the first working coil WC1 and the eccentricity determination period of the second working coil WC2 based on the driving scheme of the first working coil WC1, the driving scheme of the second working coil WC2, the duty cycle of the first working coil WC1, and the duty cycle of the second working coil WC2.

[0121] According to an embodiment of the disclosure, the driving start time and eccentricity determination period of each working coil may also be determined as in the embodiments described above in connection with FIGS. 8 to 20.

[0122] The control circuit 20 drives each of the first working coil WC1 and the second working coil WC2 at the determined driving scheme and driving start time (2110).

[0123] The control circuit 20 determines the eccentricity of the vessel placed on the first working coil WC1 according to the eccentricity determination period of the first working coil WC1 (2112). The control circuit 20 determines the eccentricity of the vessel placed on the second working coil WC2 according to the eccentricity determination period of the second working coil WC2 (2114).

[0124] The disclosure may prevent such an occasion that determination of eccentricity is rendered impossible as the respective eccentricity determination periods of working coils are set to be identical to each other in an induction heating device with the two or more working coils.

[0125] Upon determining the eccentricity of a vessel placed on any one of two or more working coils included in an induction heating device, the disclosure may prevent a lowering of output power of the other working coils, thereby enabling more stable supply of power.

[0126] Various changes in form or detail may be made to the disclosure by one of ordinary skill in the art without departing from the scope of the disclosure, and the disclosure is not limited to the above-described embodiments and the accompanying drawings.